As a method for forming a semiconductor film in a manufacturing process for a thin film transistor, a method has been widely used in which a thin film having a larger area than required is formed using a semiconductor material, and then the thin film is patterned to remove the unnecessary parts. Also, a gate electrode is often fabricated by forming a conductive thin film made of tantalum, aluminum or the like, and then patterning the thin film.
Photolithography is an example of the patterning method. In photolithography, a desired resist pattern is formed on a widely formed thin film by using a photo mask. Then, the part of the thin film not covered by the resist pattern is etched to obtain the thin film having an intended shape. In recent years, trends to realize semiconductor elements with higher integration require fabrication techniques for patterning of lines with a line width under 1 μm, so-called submicron patterning. Therefore, in etching, a method for higher resolution is used in which a finer mask pattern is formed, and an X-ray or electron beam having a shorter wavelength is used for exposure.
A thin film with a fine shape is also formed by an ink jet method. For example, methods have been proposed to discharge a solution including a semiconductor material such as an organic semiconductor material on a substrate by an ink jet discharge device, for forming a semiconductor film. In the case of discharging by the ink jet method, however, the accurate drawing of a fine pattern may be difficult depending on the wettability of the substrate surface, since discharged droplets spread over the surface. In view of the problem, methods for controlling the deposition of droplets have been proposed in which banks are formed on a substrate surface in advance in order to deposit discharged droplets in accordance with a desired pattern. The methods have been disclosed in, for example, Japanese Unexamined Patent Publications No. 59-75205 and No. 2000-353594.
However, in photolithography, equipment for forming a fine mask pattern and for exposure using an X-ray or electron beam is expensive, and throughput is low. Meanwhile, in the ink jet method, thin films on the order of submicrons are difficult to form since the diameter of droplets is typically several microns or more. In the case of using banks, photolithography and etching are necessary for forming the banks, resulting in higher costs and a lower efficiency.